1. Field of the Invention
The present invention relates generally to vehicle tires and to devices placed within the tires. More particularly, the present invention relates to apparatus and methods to generate renewable power within the tire to activate instrumentation placed within the tires. The generated power signals are also used to measure the length of the tire-to-road contact region and tire geometry that, with tire pressure, provides the tire load, the mass and center-of-mass of the vehicle, and other derived tire or vehicles values known in the field. The invention further relates to energy-optimal pulsed power capture circuits. The invention further relates to the design of run flat tires that accommodate devices mounted onto the inner tread surface for generating and capturing power or monitoring tire or vehicle status.
2. General Background and State of the Art
The Ford Explorer and Firestone Tire failures generated a great deal of interest in monitoring tires. The American automobile industry and United States Congress moved to require real-time monitoring of tire pressure to detect under-inflated tires (TREAD Act of 1 Nov. 2000). Two methods of accomplishing such monitoring have resulted: a direct method that places a pressure sensor within each tire that communicates its readings over a radio link to the main body of the vehicle; and an indirect method that monitors the rotation rates of the tires using sensors on the main body of the vehicle and infers a less inflated tire as having a higher rotation rate.
Of the two methods, the direct method is considered more accurate. It is also the most adaptable as tire temperature, tire load, and other tire sensors can be included which piggy-back their data onto the radio data link to the main body of the vehicle. Currently these devices are battery operated and, to maintain battery life over the life of the tire, are activated only intermittently. Continuous tire monitoring with this method is not practical because the battery would be drained too quickly, battery replacement is not a simple task, and high capacity batteries are too large or expensive to be accommodated within the tire.
The ability to perform rapid and nearly continuous tire monitoring is preferred and would make it possible to use the tire as a dynamic sensor and adapt the vehicle control system accordingly. There is a need to provide an apparatus and method to generate sufficient power from a renewable resource within the tire to sustain continuous or nearly continuous monitoring, or eliminate the need for a battery for intermittent monitors.
Earlier devices, such as those disclosed in U.S. Pat. No. 3,699,367 (Thomas), U.S. Pat. No. 3,760,351 (Thomas), U.S. Pat. No. 4,061,200 (Thompson), and U.S. Pat. No. 6,291,901 B1 (Cefo) couple the reciprocating radial deflation motion to a magnet or coil or fluid pump in order to generate electricity, with the disadvantage of having to attach delicate devices to the wheel inner rim where they can be damaged by installers. Others, such as the device disclosed in U.S. Pat. No. 4,504,761 (Triplett), use piezoelectric devices driven by the motion of an outer portion of the tread with respect to an inner portion, which has the disadvantage of potentially weakening the structure of the tire. U.S. Pat. No. 4,220,907 (Pappas) discloses a magnet mounted on the inner tread surface that opens and closes a magnetic flux circuit as the tread goes flat on the contact patch. U.S. Pat. No. 4,429,232 (Thomas) suggests a rotational generator mounted on a rim track and using gravity as a reference with the disadvantage of requiring a low friction track within a very dirty tire. U.S. Pat. Nos. 5,889,464, 6,175,302 (Huang) suggest piezo-electric devices driven by vibrations within the tire.
None of the cited prior art references, taken either singly or in combination, is seen to describe the present invention as disclosed and claimed.
None of the cited prior art references provide a real-time optimal method to generate maximum energy.
None of the cited prior art references provide a run flat tire adapted to support a monitoring or power generating device mounted on its inner tread surface.